In general, an optoelectronic device such as a laser is fabricated along a preferred crystallographic direction. Mirror facets for such a device are formed on a plane perpendicular to the preferred direction and sidewalls of the device are formed on planes parallel to that direction. Also, it is desirable for at least the mirror facets to exhibit the characteristic of optical flatness.
Optically flat mirror facets are created by manual cleaving or by etching. Though manual cleaving does produce high quality mirror facets, this technique yields a small number of useable cleaved facets in relation to the number of crystals actually cleaved.
Etching methods encompass both wet and dry chemical etching. Wet chemical etching techniques generally comprise several distinct phases each of which employs a particular chemical compound for etching a selected material of the multilayer structure such as an InP layer in an InGaAsP/InP system. These chemical etching techniques are generally isotropic and, therefore, are only capable of creating an extremely narrow region of optical flatness in a desired layer, for instance, the quaternary layer of the heterostructure system. Examples of wet chemical etching techniques are given in the following references: K. Iga et al., "GaInAsP/InP DH Lasers with a Chemically Etched Facet," IEEE Journal of Quantum Electronics, QE-16, p. 1044 (1980), (a solution of HCl: CH.sub.3 COOH: H.sub.2 O.sub.2 =(1:2:1)); P. D. Wright et al., "InGaAsP Double Heterostructure Lasers (.lambda.=1.3 .mu.m) with Etched Reflectors," Applied Physics Letters, Vol. 36, p. 518 (1980), (a solution of Br: CH.sub.3 OH); and S. Arai et al., "New 1.6 .mu.m Wavelength GaInAsP/InP Buried Heterostructure Lasers," Electronics Letters, Vol. 16, p. 349 (1980), (a sequential process of Br: CH.sub.3 OH followed by 4HCl-H.sub.2 O).
Dry chemical etching techniques include reactive-ion etching, reactive-ion beam etching and plasma etching. For separate descriptions of each of the above, see R. E. Howard et al., "Reactive-Ion Etching of III-V Compounds," Topical Meeting on Integrated and Guided Wave Optics Digest (IEEE: New York 1980) WA-2; M. A. Bosch et al., "Reactive-Ion Beam Etching of InP with Cl.sub.2," Applied Physics Letters, Vol. 38, p. 264 (1980); and R. H. Burton et al., "Plasma Separation of InGaAsP/InP Light-Emitting Diodes," Applied Physics Letters, Vol. 37, p. 411 (1980).
Reactive ion etching avoids some of the problems of the wet chemical etching methods and is useful in making grooves in a heterostructure system. This type of etching is effectively a single step process which results in facets which approximately planar but "overcut". That is, the facets which form the groove slope toward each other from the top of the groove to the bottom. Although these facets are reproducible, they lack the optically flat mirror quality necessary for certain applications. Similarly, the other dry etching techniques create facets satisfactory for use as waveguide sidewalls and die separations but lacking the optically flat mirror quality necessary for optoelectronic and integrated optics devices.